Synthetic resins have long been widely used for building materials, automobile parts, packaging materials, agricultural materials, housing materials for home electronics and toys due to their chemical and mechanical properties. However, many synthetic resins are combustible, and depending on their use, they did not have sufficient flame-retarding properties. Flame retarding properties may be conferred by inorganic phosphorus flame retardants, e.g., halogen flame retardants, red phosphorus or polyphosphate type flame retardants such as ammonium polyphosphate, organic phosphorus type flame retardants such as triaryl phosphate esters, metal hydroxides or antimony oxide which is a flame retarding auxiliary agent, and melamine compounds. The use of these substances, alone or in combination, is well-known.
Among these, halogen flame retardants have a superior flame retarding effect, but since they generate toxic substances such as hydrogen halide gases and dioxin during combustion, a flame retarding method which did not use a halogen flame retardant was desired. In the case of metal hydroxides such as magnesium hydroxide, a flame retarding effect was not obtained unless a large amount was used, so the workability of the resin and the physical properties of molded items produced from it were impaired. In the case of phosphorus flame retardants, phosphate esters which are excellent for conferring flame retarding properties on polycarbonates, and inorganic phosphorus flame retardants which are excellent for conferring flame retarding properties on polyolefins, are used. Inorganic phosphorus flame retardants such as ammonium polyphosphate, useful for conferring flame retarding properties on polyolefins which are general-purpose resins, are easy to form a secondary aggregation and interfere with their dispersion in the resin, therefore, when the resin is molded into films or fibers, the molding apt to have defects. Also ammonium polyphosphate hydrolyzes, so its hygroscopic properties had to be reduced.
As a means to control the aggregation and hygroscopic properties of ammonium polyphosphate, which is an inorganic phosphorus flame retardant, Japanese Unexamined Patent Publication tokkai-syo 61-98722 (refer to claims) discloses a polyurea coating, tokkai-syo 61-103962 (refer to claims) discloses a melamine/formaldehyde resin coating, tokkai-hei 3-131508 (refer to claims) discloses a curable silicone resin coating, European Patent No. 93993 (refer to claims, in particular claim ) discloses an epoxy resin coating, and Japanese Unexamined Patent Publication tokkai-hei 8-134455 (refer to claims) discloses the blending of microfine silica coated with a silicone oil.
However, in the aforesaid coating method proposed by tokkai-hei 3-131508, the flame retardant is treated in an organic solvent, so manufacturing costs are high, and solvent and effluent treatment are also required. Therefore, a treatment method which could be performed without a solvent was desired.
In Japanese Unexamined Patent Publication tokkai 2003-26935 (refer to claims), it is stated that a superior flame retarding effect is achieved with only a small amount of flame retardant by concurrent use of complex salt of polyphosphoric acid, melamine and piperazine with a drip inhibitor. Since this flame retardant not only had a superior flame retarding effect but also superior water resistance, it was easy to handle compared with ammonium polyphosphate.
However, in resins which had been treated with the flame retardant described in tokkai 2003-26935 (refer to claims), the electrical resistance decreased with time considerably, so it could not be used for applications in which stable electrical properties were required.
As an efficient surface treatment method, tokkai 2000-63842 (refer to claims) proposes modifying the surface of ammonium polyphosphate and melamine polyphosphate flame retardants by applying a solvent containing composition of a silicon containing coating agent or a water-soluble organopolysiloxane to the flame retardant particles. However, there is no mention of piperazine polyphosphate, nor any postulation that the flame retardant obtained by combining piperazine polyphosphate and melamine polyphosphate offered superior flame retarding properties when treated with silicone oil, nor that the flame retardant can be obtained without impairing the electrical properties of the blended resin.